Specific "recognition" between biological molecules plays a fundamental role in most processes in living cells: recognition between two complementary strands of DNA or RNA, between DNA and histones, between carcinogens and DNA, between DNA and repressors, between enzymes and substrate, etc. To understand the mode of recognition, it is necessary to know the three dimensional structure of the molecular complex involved, or the corresponding model complex at the atomic resolution. The overall objectives of this research proposal are to do x-ray crystallographic studies on model or true molecular complexes between nucleic acids and various interacting molecules such as aromatic carcinogens, mutagens and dyes; protamines and peptides; oligonucleotides and deoxyoligonucleotides. This is a supplemental request for a fund to cover 1/3 of a diffractometer and the principal investigator's summer salary.